ts-prime/src/splitAt.ts

A utility library for JavaScript and Typescript.

import { purry } from './purry';

/**
 * Splits a given array at a given index.
 * @param array the array to split
 * @param index the index to split at
 * @signature
 *    P.splitAt(array, index)
 * @example
 *    P.splitAt([1, 2, 3], 1) // => [[1], [2, 3]]
 *    P.splitAt([1, 2, 3, 4, 5], -1) // => [[1, 2, 3, 4], [5]]
 * @data_first
 * @category Array
 */
export function splitAt<T>(array: readonly T[], index: number): [T[], T[]];

/**
 * Splits a given array at a given index.
 * @param array the array to split
 * @param index the index to split at
 * @signature
 *    P.splitAt(index)(array)
 * @example
 *    P.splitAt(1)([1, 2, 3]) // => [[1], [2, 3]]
 *    P.splitAt(-1)([1, 2, 3, 4, 5]) // => [[1, 2, 3, 4], [5]]
 * @data_last
 * @category Array
 */
export function splitAt<T>(index: number): (array: readonly T[]) => [T[], T[]];

export function splitAt() {
  return purry(_splitAt, arguments);
}

function _splitAt<T>(array: T[], index: number) {
  const copy = [...array];
  const tail = copy.splice(index);
  return [copy, tail];
}